Healing of the infarcted heart is dependent on an inflammatory reaction that serves to clear the wound from dead cells and matrix debris, while activating reparative pathways. Transforming Growth Factor (TGF)- is induced and activated in the infarcted myocardium and critically regulates the reparative, fibrotic and remodeling responses through cell-specific actions that involve a family of intracellular effectors, the Smads TGF- may also signal through activation of Smad-independent pathways. Targeting TGF- in infarcted and failing hearts holds therapeutic promise; however, implementation of such approaches requires dissection of the cellular effects of Smad and non-Smad signaling cascades. This competing renewal application studies the role of TGF- signaling pathways in the infarcted heart. Using cell-specific knockout mice and in vitro strategies we will explore the cell biological effects and functional consequences of TGF-/Smad signaling in the remodeling infarcted myocardium. Our unpublished preliminary data suggest crucial and distinct effects of Smad-dependent signaling on cardiomyocytes, fibroblasts and macrophages; these actions have opposing effects on post-infarction cardiac remodeling. Our experiments will dissect the role of Smad2 and Smad3 signaling in fibroblasts, macrophages and cardiomyocytes: Specific aim 1 will study the in vivo role of fibroblast-specific Smad-dependent signaling in repair and remodeling of the infarcted heart. Using mice with cell-specific loss of Smad2 or Smad3 in activated myofibroblasts (generated by our laboratory), we will investigate the role of fibroblast Smad signaling in repair, remodeling and function of the infarcted heart and we will dissect the molecular basis for Smad-dependent actions. Specific aim 2 will dissect the effects of Smad-dependent and non-Smad signaling on cardiac fibroblast phenotype and function. Cardiac fibroblasts will be cultured in collagen pads in order to explore and dissect cell:matrix interactions. Specific aim 3 will investigate the role of macrophage Smad2 and Smad3 signaling in repair and remodeling of the infarcted heart using mice with cell-specific loss of Smad2/3. Moreover, in vitro studies will investigate the effects of Smad cascades on macrophage differentiation, phenotype, and function. Specific aim 4 will study the role of cardiomyocyte-specific Smad2 and Smad3 in injury, repair and remodeling of the infarcted heart using cell-specific KOs. Cardiomyocyte Smad signaling may modulate apoptotic cascades, may trigger a hypertrophic program, or may mediate paracrine actions of cardiomyocytes, responsible for adverse remodeling.